Hi mat10x,

thanks! you will find the hidden .mp3 file when you download
the steg program from my download link and then run the
command (in a Terminal or cmd.exe):

steg show -input hidden.3dm -outputdir path/to/dir

Regarding the modeling i did that many years ago,
so i can't help that much, because i forgot the steps.

Only thing i remember is that i used also ViaCAD
for this model to get the proper N-Sided Surface
at the tail.

Regards
Stefan